With a spread of air-bags and a mandatory requirement to use a seat-belt, a death toll from car traffic accidents is inclining to decrease. However, a number of traffic accidents and a number of persons injured tend to still increase due to an increase of senior drivers along with aging of the society. Under such background, a sensor that detects obstacles around a car to assist driving is now attracting attention, and ultrasonic sensors, cameras, millimeter-wave radars and the like are been commercialized until now.
While a conventional in-vehicle radar system can detect obstacles located in a middle range of 30 meter or less or in a long range of 150 meter or less, the radar system has a problem that its detection error is significant for an obstacle located in a short range of 2 meter or less for example. Accordingly, in order to be able accurately detect obstacles located around the car, it is requested to put an UWB radar that assures a high distance resolution and a wide view field coverage into practical use.
Patent Document 1 discloses an array antenna configured by arraying element antennas by 2×4 . The array antenna can measure an azimuth angle in a horizontal direction by a phase comparison monopulse method when it is used as a receiving antenna of the UWB radar. It is also possible to use these element antennas as a transmitting antenna by arraying by 1×4. Such an in-vehicle radar system is strongly demanded so as to be able to realize a wide coverage of a radiation pattern in the horizontal direction and to downsize to improve a space factor. Then, there is a need for a transmitting and receiving integrated antenna configured by disposing and integrating transmitting and receiving antennas on one substrate.